The disclosure relates generally to pressure relief valves, and more particularly, to valve pressure assemblies that maintain a pressure of a thief hatch while the thief hatch is open and in an operative state.
Storage tanks, such as an above-ground or below-ground storage tank, may include openings designed to accept a venting device, such as a thief hatch, to provide access to the interior of the storage tank. For example, the thief hatch may provide a resealable opening through which a tool may be inserted into the interior of the storage tank.
The internal pressure (for example, internal vapor pressure) of storage tanks may vary and may depend on various factors, such as the amount of fluid in the storage tank, the volatility of the fluid in the storage tank, the temperature of the fluid in the storage tank, the temperature outside the storage tank, and the thermal conductivity of the walls of the storage tank. Accordingly, excessive vapor pressure in the storage tank may be relieved in a controlled fashion. For example, a thief hatch may provide a seal that blocks fluid communication between the interior of the storage tank and the exterior of the storage tank when the vapor pressure within the tank is below a threshold and enables fluid communication between the interior of the storage tank and the exterior of the storage tank when the vapor pressure within the tank is above the threshold.
Some thief hatches include a seal assembly to prevent leakage of the fluid and/or vapors around and/or through a valve or a valve seat. Conventional seal assemblies include an inner gasket coupled near the valve seat and outer gasket coupled near a cap 32 or lid of the thief hatch. When the cap 32 is closed, the inner gasket facilitates sealing the valve seat to keep the vapors/fluid within the storage tank. Moreover, when the cap 32 is closed, the outer gasket facilitates sealing the cap 32 to the keep any vapors/fluid that has passed the inner gasket from escaping the cap 32. The inner gasket and the outer gasket prevent vapor/fluid leakage from the storage tank and into the atmosphere or surrounding environment. Over time the inner gasket and/or outer gasket break down which can lead to fluid or vapor discharge and reduced pressurization of the storage tank. Moreover, the vapor/fluid may discharge into the atmosphere and/or surrounding environment leading to health and environmental issues. For safety, environment, and/or maintenance reasons, the gaskets may require maintenance inspection and/or replacement.
During typical maintenance and/or replacement inspections, a worker disconnects the cap 32 of the thief hatch and rotates the cap 32 to an open position. In the open position, the pressure of the actuating number, for example a spring, of the thief hatch is released. Since the biasing pressure is released, the pressure of the vapor or fluid present in the storage tank may discharge through the thief hatch valve to expose the worker to dangerous vapors and/or fluids. Moreover, the discharged vapor and/or fluids flow into the atmosphere or surrounding environment leading to environmental issues. Additionally, with the biasing pressure of the actuating mechanism released, it may be difficult for the worker to determine if the inner gasket has failed. More particularly, since the internal pressure may be released through the thief hatch valve, the inner gasket is not exposed to the full internal pressure to show leakage or failure signs. Accordingly, the worker typically replaces both the inner gasket and the outer gasket in an abundance of caution. The typical replacement procedure may lead to increased effort, time, material, and/or exposure for the worker.
Accordingly, it would be advantageous to open a thief hatch cap while maintaining the actuating mechanism of the thief hatch in a pressurized or operative state/position. Moreover, it would be advantageous to open a thief hatch cap to provide visual and/or physical access to the inner gasket and the outer gasket while maintaining the internal pressure of the storage tank. Additionally, it would be advantageous to provide a safer, efficient, and sounder process for inspection, maintenance, and/or replacement of the inner gasket and/or the outer gasket.